Well in terms of talent, the X-Man must top the list, but in terms of mental toughness and the player who is the likeliest to claim a title in the near future, I'd have to go for Nieminen - he's highest-ranked, he's been in four career finals, he's a strong and determined competitor, which is more than you can say for Greaseball Malisse... I don't want to suggest that I dislike the man or anything, but somebody call me the moment he wins a title, I reckon we'll have to wait a long time...
And don't forget Vince, of course - how fitting that the man dubbed a serial loser and a quintessential journeyman in fact has nary a title to his name.